Hepatitis C virus (HCV) is one of the leading causative agents of chronic hepatitis and cirrhosis. HCV infection of liver is associated with the development of hepatocellular carcinoma. It is estimated that about 4 million people in the US are infected with HCV. The RNA genome of this virus encodes a polyprotein of 3010 amino acids. HCV RNA genome consists of unique sequences and structures at its 5' and 3' termini, which are essential features required for viral translation and replication. The RNA genome codes for three structural proteins and at least six nonstructural proteins. One of the nonstructural proteins, NS5A has generated significant levels of interest due largely to its suggested role in interferon-resistance. In this application, we propose to investigate the functions associated with the HCV NS5A. Translation and replication functions of the HCV RNA genome are associated with the ER membrane. These activities in the ER induce ER stress and ER overload responses. ER stress leads to unfolded protein response (UPR), which leads to activation of whole host of ER chaperone proteins. The ER overload response appears to involve two second messengers, calcium and reactive oxygen species. Their activities ultimately lead to the activation and translocation of transcription factors to the nucleus whereupon they bind cognate DNA sequences and regulate gene expression. NF-kappaB and STAT-3 are two such transcription factors which are activated by phosphorylation and are transported to nucleus. Herein, we propose to investigate the mechanism of activation of ER-nucleus signal transduction pathway by the HCV NS5A. These studies have the potential to provide information of direct relevance to the chronic liver disease pathogenesis including its progression to hepatocellular carcinoma associated with the HCV infection.